Optical fibers are a kind of signal transmission means based on the principle of full reflection. Optical fibers are inexpensive because the main raw material of optical fibers is silicon, the reserves of which are large in the surface of the Earth. Optical fibers have been widely utilized in society for applications such as communications, and also significantly used in the field of medicine and entertainment.
High-power fiber lasers are a kind of small-sized laser systems, with the advantages of being easy to carry and set up, high electro-optical conversion efficiency, good beam quality, and being easy to dissipate heat, and so on. High-power fiber lasers have been widely utilized in applications such as cutting, welding, drilling, surface treatment, etc., and are the fastest growing laser products in recent years. However, unwanted residual pump energy generally exists before the laser light enters the laser source output (i.e., output collimator) of the high-power fiber laser. The residual pump energy, if not removed, will directly degrade the beam quality of the laser source that is outputted. The degraded beam quality and abundant heat load may cause damage to the output collimator; and even worse, the entire laser system would be destroyed because the residual laser light reflected by the output collimator is fed back to the laser system.
The conventional solutions to the above problems include a high refractive index coating (glue) method. In general, a passive double cladding layer fiber structure is composed of a fiber core, an inner cladding layer, and an outer cladding layer. The high refractive index coating (glue) method is to apply a polymer glue material, having a refractive index equal or greater than that of the material of the inner cladding layer, to the surface of the inner cladding layer. The working principle of this method is to direct the residual pump lights within the cladding layer out of the inner cladding layer by applying the optical refraction and scattering effects; to convert the light into heat by absorption through glue material and thermal packaging mechanism design; and finally to dissipate the heat by applying air-cooling or water-cooling, thus achieving the purpose to remove residual cladding energy. However, the residual scattering light directed by this method may cause temperature increase of the polymer glue material. General polymer glue material can withstand the temperature up to 90 to 100° C., and will burn when the temperature is greater than 150° C. Hence, this method can be applied to residual pump light energy of about 100 W, but does not apply to multi-kilowatt fiber laser systems.
Therefore, the industry is currently in great need to develop a cladding power stripper for high-power fiber, with the heat dissipation mechanism of good thermal efficiency to eliminate the unwanted residual pump energy before the laser light entering the output collimator of the high-power laser. It is desirable to achieve both the quality and efficiency of the laser light, and to avoid the destruction of the entire laser system due to the residual laser light reflected by the output collimator.